1. Field of the Invention
The present disclosure relates to an inorganic binder composition for casting, and more particularly to an eco-friendly inorganic binder composition for casting which is supplemented in strength and water resistance so as to be suitable for a climate of high temperature and high humidity and improved in sand burning by including nano-silica, a Li-based water resistant additive, an organic silicon compound, and an anti-sand burning additive in water glass.
2. Description of the Related Art
Korean casting foundry industry has greatly contributed to all kinds of industries including shipbuilding industry, auto-parts industry, industrial machine industry, construction machine industry, and the like. Although the casting foundry industry is an important basic industry indispensable for the development of national industry, the current environment surrounding the casting foundry industry, such as environmental problems, price fluctuations in subsidiary materials, policies, lack of manpower, and the like, is not very good. Above all, the environmental problems have been set as a priority to be solved. Currently, in the casting industry, environmental pollution has been improved in order to block discharge of environmental pollutants generated during a metal dissolution process, a core manufacturing process, and a casting process. However, since the casting industry has been regulated in greenhouse gas emission by the Muskie Act, the Kyoto Protocol, and the like, a method for getting rid of discharge of basic pollutants and a technical method for reduction in energy consumption, improvement in working environment, and greening of manufacturing sites have been urgently needed.
That is, an organic binder has been widely used for years from mass production to molding of a small-sized product and a multi-shaped core, but the organic binder generates toxic steam during molding of a core and also generates a VOC material such as benzene and carbon dioxide during disassembling of a cast, and, thus, has a bad influence on the environment. Furthermore, the organic binder requires a large amount of thermal energy for sintering, and it is difficult to reclaim sand due to a residue of ash or carbon within a molded object. Accordingly, an eco-friendly inorganic binder has been developed in order to solve the environmental problem and improve productivity of cores.
An inorganic binder makes it possible to perform a curing process at a low temperature and does not generate a toxic substance, and, thus, a working environment is kept in a good condition. Furthermore, just a small amount of a gas is generated during a manufacturing process of a core and a casting process, and, thus, defects in casting are reduced, and there is no need to install an anti-environmental pollution system, and, thus, manufacturing costs can be reduced.
In this regard, Korean Patent Laid-open Publication No. 10-2011-0106372 discloses a technique of using an inorganic binder for manufacturing a sand cast and a core by mixing sand with sodium hydroxide and tetraethylsilicate. Furthermore, Korean Patent No. 10-1027030 discloses a technique of using a suspension including a sodium hydroxide solution, alkali silicate with a solid content of 70%, and amorphous spherical silicon dioxide, and European Patent No. 1057554 discloses a technique for producing a casting mold and a core by using a two-component binder system including alkyl silicate and an alkyl silicate oligomer.
However, the above-described inorganic binder has been developed by adding various additives into water glass as a main material and it is eco-friendly and improved in moldability and fluidity, but weak in water resistance due to a hygroscopic property of the water glass. Therefore, the above-described inorganic binder has problems of swelling, a decrease in strength, and elution caused by moisture, and, thus, cannot be used in a climate of high temperature and high humidity.
Furthermore, the inorganic binder for casting is in liquid form based on the water glass (xSiO2-yNa2O) and lacks a thermal property and thermal resistance. Thus, there occurs sand burning caused by the remaining sand on a metal surface during disassembling of a cast.
In this regard, Korean Patent Laid-open Publication No. 10-2013-0102982 discloses a technique for preventing sand burning by adding spherical iron oxide. Furthermore, Korean Patent No. 10-1027030 discloses a technique for increasing the strength of a core and preventing sand burning by separately inputting SiO2 dispersed in a liquid.
As described above, a technique for preventing sand burning by adding a granular anti-sand burning additive has greatly contributed to commercialization of eco-friendly inorganic binders, but the use thereof has been avoided in the industrial site due to addition of a process in view of productivity and safety in management of additives and storage of binders.
Therefore, in view of the foregoing, the inventors of the present disclosure developed a commercializable eco-friendly inorganic binder composition for casting which has a good fluidity and is supplemented in strength and water resistance so as to be suitable for a climate of high temperature and high humidity and improved in sand burning by including nano-silica, a Li-based water resistant additive, an organic silicon compound, and an anti-sand burning additive in water glass, and completed the present disclosure.